The territory of France was part of the Celtic area under the Roman empire. It was conquered by the Franks in the 5th century. France became one of the leading nations in Europe. It was a monarchy until the revolution of 1793, and has been a republic since 1871. It developed a colonial empire, with large territories in Africa, Asia, the Pacific and the Americas. In the 20th century, France experienced the devastation of two world wars, and fought two colonial wars in Indochina and Algeria. A founding member of the European Union, the country has established itself as one of the major political and economic powers in the world. France was Christianized in the 5th century. The Catholic Church in France has been one of the main centres of western Christianity, and is the majority church. France was the birthplace of the Calvinist Reformation, but Protestantism has remained a minority. As a result of the Enlightenment and the French revolution, a particular concept of separating the temporal and the spiritual developed in France, called "laïcité". Islam has become the second religion, because of immigration, which has also brought many African Christian communities. The Protestant Federation of France embraces a wide variety of denominations, including Evangelical and Pentecostal groups. The Assemblies of God, the largest Pentecostal church, is not part of the Federation. The Council of Christian Churches groups together the Catholic Church, the Protestant Federation and the Orthodox churches. There is also an Evangelical Alliance, affiliated with the WEA. A survey in 2006 is showing a slight increase in the number of Protestants in France, mainly due to the growth of the Evangelical churches, especially those of African origin.